PlatformTransactionManager
implementation for a single JDBC DataSource. This class is
capable of working in any environment with any JDBC driver, as long as the setup
uses a JDBC 2.0 Standard Extensions / JDBC 3.0 javax.sql.DataSource
as its Connection factory mechanism. Binds a JDBC Connection from the specified
DataSource to the current thread, potentially allowing for one thread-bound
Connection per DataSource.

Note: The DataSource that this transaction manager operates on needs
to return independent Connections. The Connections may come from a pool
(the typical case), but the DataSource must not return thread-scoped /
request-scoped Connections or the like. This transaction manager will
associate Connections with thread-bound transactions itself, according
to the specified propagation behavior. It assumes that a separate,
independent Connection can be obtained even during an ongoing transaction.

Application code is required to retrieve the JDBC Connection via
DataSourceUtils.getConnection(DataSource) instead of a standard
J2EE-style DataSource.getConnection() call. Spring classes such as
JdbcTemplate use this strategy implicitly.
If not used in combination with this transaction manager, the
DataSourceUtils lookup strategy behaves exactly like the native
DataSource lookup; it can thus be used in a portable fashion.

Alternatively, you can allow application code to work with the standard
J2EE-style lookup pattern DataSource.getConnection(), for example for
legacy code that is not aware of Spring at all. In that case, define a
TransactionAwareDataSourceProxy for your target DataSource, and pass
that proxy DataSource to your DAOs, which will automatically participate in
Spring-managed transactions when accessing it.

Consider defining a LazyConnectionDataSourceProxy for your target
DataSource, pointing both this transaction manager and your DAOs to it.
This will lead to optimized handling of "empty" transactions, i.e. of transactions
without any JDBC statements executed. A LazyConnectionDataSourceProxy will not fetch
an actual JDBC Connection from the target DataSource until a Statement gets executed,
lazily applying the specified transaction settings to the target Connection.

On JDBC 3.0, this transaction manager supports nested transactions via the
JDBC 3.0 Savepoint mechanism. The
"nestedTransactionAllowed" flag defaults
to "true", since nested transactions will work without restrictions on JDBC
drivers that support savepoints (such as the Oracle JDBC driver).

This transaction manager can be used as a replacement for the
JtaTransactionManager in the single
resource case, as it does not require a container that supports JTA, typically
in combination with a locally defined JDBC DataSource (e.g. a Jakarta Commons
DBCP connection pool). Switching between this local strategy and a JTA
environment is just a matter of configuration!

DataSourceTransactionManager

setDataSource

public void setDataSource(javax.sql.DataSource dataSource)

Set the JDBC DataSource that this instance should manage transactions for.

This will typically be a locally defined DataSource, for example a
Jakarta Commons DBCP connection pool. Alternatively, you can also drive
transactions for a non-XA J2EE DataSource fetched from JNDI. For an XA
DataSource, use JtaTransactionManager.

The DataSource specified here should be the target DataSource to manage
transactions for, not a TransactionAwareDataSourceProxy. Only data access
code may work with TransactionAwareDataSourceProxy, while the transaction
manager needs to work on the underlying target DataSource. If there's
nevertheless a TransactionAwareDataSourceProxy passed in, it will be
unwrapped to extract its target DataSource.

The DataSource passed in here needs to return independent Connections.
The Connections may come from a pool (the typical case), but the DataSource
must not return thread-scoped / request-scoped Connections or the like.

doGetTransaction

The returned object will usually be specific to the concrete transaction
manager implementation, carrying corresponding transaction state in a
modifiable fashion. This object will be passed into the other template
methods (e.g. doBegin and doCommit), either directly or as part of a
DefaultTransactionStatus instance.

The returned object should contain information about any existing
transaction, that is, a transaction that has already started before the
current getTransaction call on the transaction manager.
Consequently, a doGetTransaction implementation will usually
look for an existing transaction and store corresponding state in the
returned transaction object.

isExistingTransaction

Check if the given transaction object indicates an existing transaction
(that is, a transaction which has already started).

The result will be evaluated according to the specified propagation
behavior for the new transaction. An existing transaction might get
suspended (in case of PROPAGATION_REQUIRES_NEW), or the new transaction
might participate in the existing one (in case of PROPAGATION_REQUIRED).

The default implementation returns false, assuming that
participating in existing transactions is generally not supported.
Subclasses are of course encouraged to provide such support.

doCommit

An implementation does not need to check the "new transaction" flag
or the rollback-only flag; this will already have been handled before.
Usually, a straight commit will be performed on the transaction object
contained in the passed-in status.

doRollback

An implementation does not need to check the "new transaction" flag;
this will already have been handled before. Usually, a straight rollback
will be performed on the transaction object contained in the passed-in status.

doSetRollbackOnly

Set the given transaction rollback-only. Only called on rollback
if the current transaction participates in an existing one.

The default implementation throws an IllegalTransactionStateException,
assuming that participating in existing transactions is generally not
supported. Subclasses are of course encouraged to provide such support.